A projection-type image display apparatus (projector) for displaying images on a large screen is used highly frequently at presentations in such places as conference halls and assembly rooms. In a conventional projector, a large-sized light source typified by a halogen lamp or a metal halide lamp is adopted for the purpose of use at presentations to a relatively large audience.
In recent years, however, there has been an increasing demand for a type of projector that is connected to or incorporated in a mobile phone terminal or a notebook PC for the purpose of use at presentations to a few or several viewers. In this trend, particular attention is being given to a projector equipped with light emitting elements (light emitting diodes (LED) or semiconductor lasers) as light sources to display an image by raster-scanning light beams from the light emitting elements. Such a projector is called a “micro-projector” because of the size thereof. In operation of the micro-projector, light beams having wavelengths that approximately correspond to three RGB primary colors (red, blue, green) from light emitting elements are raster-scanned across a screen or applied thereon to provide still image projection.
A projector of a common type is designed to operate in a fashion that light beams emitted from RGB light sources are scanned by using an optical part such as an MEMS (micro electro mechanical systems) mirror for direct projection onto a screen. In the case of a projector using laser light beams, since each of RGB light sources can be controlled independently, there is no need to use RGB subpixels for forming each pixel as required in a flat display panel such as is represented by a liquid crystal display panel. In optical axial alignment of the projector using laser light beams, RGB beam positions are superposed on a screen so as to form a white beam spot thereon.
Japanese patent document JP-A-2008-309935 discloses a technique for optical axial alignment by using two dichroic mirrors in projection of spatially propagating light beams from R, G, and B light sources.